In 1900, at age 21, Einstein had his university diploma and was eager to begin his career as a physicist. He struggled to find work, however. After two years of searching, Einstein took a relatively low-level job at the patent office in Bern, Switzerland. Glad for the income and steady work reviewing patent applications--and still able to think about physics after hours—Einstein settled into a comfortable routine. Each day he walked to work through the streets of Bern, a city famous for its medieval architecture and beautiful clock towers.
Einstein passed by the clock towers again on his way home, a route he often took with his closest friend, Michele Besso. The two men regularly discussed science and philosophy—including the nature of time. After one such discussion, Einstein came to a sudden realization: Time is not absolute. In other words, despite our common perception that a second is always a second everywhere in the universe, the rate at which time flows depends upon where you are and how fast you are traveling. Einstein thanked Besso in his first paper on the Special Theory of Relativity.
Time does not progress at the same rate for everyone, everywhere. Instead, Einstein showed that how fast time progresses depends on how fast the clock measuring time is moving. The faster an object travels, the more slowly time passes for that object, as measured by a stationary observer.
Earth is traveling at 107,000 kilometers (67,000 miles) an hour around the Sun. You are standing still, but only in relation to Earth. Relative to the Sun, you are traveling through space very quickly. Physicists use the phrase "relative motion" to convey the idea that whether an object is at rest or in motion depends on your point of view--or your "frame of reference."
Time seems to follow a universal, ticktock rhythm.
But it doesn't.
In the Special Theory of Relativity, Einstein determined that time is relative--in other words, the rate at which time passes depends on your frame of reference.
What time is it?
That depends on how fast you're traveling.
Thanks to Einstein, we know that the faster you go, the slower time passes--so a very fast spaceship is a time machine to the future.
An essential element of exciting science fiction is voyaging to the far reaches of the universe. But with current technology, a trip to the closest star, Alpha Centauri, would take more than 80,000 years!
Much faster ships, traveling at a significant percentage of the speed of light, would shorten the journey.